The present invention relates to an axial flow fan, and more particularly to an axial flow fan with improved blades having advantages of ultra-thin dimension, low noise level high air flow, and high fan pressure, which is especially suitable for use in office automation Machines.
In a conventional axial flow fan, it is generally, composed of a driving motor, a cylindrical central section, a plurality of blades, and an outer casing for casing the fan. Each of the blades extends radially outward from the cylindrical hub section of the fan. A motor shaft the driving motor is attached to the hub section at a central aperture of the hub and thus the hub section may be rotated by the driving motor via the motor shaft. In such an arrangement, the hub section together with the blades may rotate about an axis of the outer casing in order to force air flow from inlet area to outlet area of the fan. The motor rotates the blades of the fan via the motor shaft so as to make the blades generate lift force which is in a form fan pressure and air flow.
It is known that the attack angle, camber angle, blade angle, pitch-chord ratio, and the shape of the blades are possible factors of affecting the lift force of the blades described above. In addition, the outer shape dimension of the blades also effects the features of the axial fan
In the prior art, the above mentioned problems caused by the improper design relating to the lift force of the blades are as follows:
1. Improper Attack Angle
The different designs of the blade shape may result in different effective ranges of the attack angle and different lift factor of the blade. If the attack angle exceeds a proper value, it is highly possible to result in stall and greater noise. On the contrary, if the attack angle is improperly designed less than a proper value, it will be affect the lift force of the blade and correspondingly result in lower performance efficiency.
2. Improper Camber Angle
In theory, the larger the camber angle, the greater the lift force under a condition of constant attack angle. However, in practice, the attack angle will be correspondingly decreased in accordance with the increase of the camber angle. Consequently, the attack angle and the camber angle must be balanced to a proper value therebetween to get a best lift factor.
3. Improper Blade Angle
Under a condition of constant rotation speed, the blade angle exceeds or less than a proper value may result in the loss of the lift force.
4. Improper Chord-pitch Ratio Distribution
The improper design of the pitch-chord ratio may result in loss of the lift force of the fan. In practice, the chord-pitch ratio is less than 1 in order to be more convenient to be manufactured. It is found that the improper chord-pitch ratio distribution may result in fluid interference to the air flow. In addition, improper chord-pitch ratio also causes lower performance efficiency of the fan and make it difficult to minimized the outer casing of the fan.
Various prior U.S. patents had been developed in this field. For example, U.S. Pat. Nos. 4,971,520 and No. 4,569,631 disclosed an axial fan. However, the prior art patent can not effectively overcome the problems described above, especially the difficulty of minimizing the thickness of the outer casing.